The present invention relates to a cathode-ray tube, and more particularly to a cathode-ray tube in which a flatness of image is improved in the effective region of panel to enhance the visual recognition, and a color selecting electrode (shadow mask) can be worked or shaped easily.
Generally, a cathode-ray tube has a vacuum envelope made of a glass panel having a substantially rectangular face plate and glass funnel. In this cathode-ray tube, the electron beam emitted from an electron gun arranged in the neck of the funnel is deflected by a deflection yoke provided on the funnel, the deflected electron beam is directed to a substantially rectangular fluorescent screen formed on an inner effective region of the face plate, and the screen is scanned by the electron beam horizontally and vertically so that an image is displayed on the screen. In a color cathode ray tube, in particular, the fluorescent screen formed on the effective region of the panel is composed of three color fluorescent layers emitting in blue, green and red light rays, and instead of the electron gun for generating a single electron beam, an electron gun structure or assembly for emitting three electron beams is provided in the neck of the funnel. The three electron beams emitted from the electron gun assembly are deflected by the deflection yoke, and so pass through the shadow mask as to be selectively directed to the corresponding fluorescent layers. The fluorescent screen is scanned horizontally and vertically by these electron beams so that a color image is displayed on the screen.
Such a cathode-ray tube is preferably designed to be flat in the effective region of the panel and the fluorescent screen from the viewpoint of ease of observing the image. There have been already attempted about flattening of the panel, but there are many problems in the conventional art that strength of the vacuum envelope made of glass is decreased, and, in the color cathode ray tube, the shadow mask can not be easily shaped into a flat structure and vibration may be occurred on the shaped shadow mask. Thus it is a contradictory problem to improve the flatness of the panel to enhance the visual recognition and the image characteristic and to maintain the mechanical characteristic of the panel and the shadow mask.
Jpn. Pat. Appln. KOKAI Publication No. 7-99030 discloses a color cathode ray tube having the flat inner and outer surfaces of the effective region of the panel. However, when the effective region of the panel is formed in a flat surface, in order to compensate for the strength of the vacuum envelope, even if the side wall of the panel is tightened by a conventional reinforcement band, the strength of the vacuum envelope is not assured. That is, in the conventional panel which is so formed as to have a convex surface projecting in the outward direction in the center of at least the inner surface of the effective region, the side wall is tightened by a reinforcement band so that the convex surface of the inner surface of the effective region can be held. Thus, it is possible to compensate for the distortion of sinking of the central part of the effective region which may be caused under the atmospheric pressure. However, in the panel having a flat surface in the inner surface of the effective region, since the central part sinks, the compensation action can not be obtained. In such a panel, accordingly, it is required to glue a safety panel or the like to the outer surface of the effective region, which results in added thickness or added cost of the panel. In particular, thickening of the panel deteriorates the visual recognition of flatness due to the floating phenomenon of image in the peripheral area of the screen by refraction of light rays in the panel glass as discussed later. Further, corresponding to the inner surface of the effective region of the panel, it is also necessary to flatten the effective surface of the shadow mask, but as compared with the curved shadow mask, the flattened shadow mask is inferior in workability, and the cost may be increased.
To solve the problem of floating phenomenon of image in the peripheral area due to refraction of light rays in the panel glass mentioned above, Jpn. Pat. Appln. KOKAI Publication No. 6-36710 discloses a cathode-ray tube having a constitution in which the effective region of the panel is formed in the concave lens structure to compensate for floating of image in the peripheral area of the screen.
However, in the panel curved in the inner surface of the effective region of the panel to such a limit as to apply the shadow mask having the effective surface formed in a curved surface, if such concave lens structure is applied, the thickness of the peripheral part of the effective region is too thick, and the transmittance in the peripheral area is degraded, and the visual recognition of the flatness relative to the viewpoint remote from the tube axis is increasingly decreased.
Jpn. Pat. Appln. KOKAI Publication No. 6-44926 discloses a cathode-ray tube having a safety panel glued through a transparent resin layer to the outer surface of a panel whose outer surface is substantially a flat surface and whose inner surface is a curved surface having a certain curvature in the horizontal and vertical direction.
In the cathode-ray tube having such structure, it is possible to compensate for the strength of the vacuum envelope. However, the transmittance is decreased in the peripheral area, and the problem of deterioration of visual recognition of flatness relative to the viewpoint remote from the tube axis can not be solved.
Further, Jpn. Pat. Appln. KOKAI Publication No. 9-245685 discloses a cylindrical cathode-ray tube whose outer surface is substantially a flat surface and whose inner surface is a curved surface in the horizontal direction, and Jpn. Pat. Appln. KOKAI Publication No. 10-64451 discloses a color cathode ray tube having a curved surface whose radius of curvature in the horizontal direction is infinite and radius of curvature in the vertical direction is fixed. In particular, Jpn. Pat. Appln. KOKAI Publication No. 10-64451 shows the color cathode ray tube whose wall thickness in the peripheral area of the effective region of the panel is about 1.2 to 1.3 times that of the central part in consideration of floating of image due to refraction of light rays by the panel glass. Actually, however, by the wall thickness difference of such degree, the strength of the vacuum envelope by the reinforcement band can not be obtained sufficiently, and it is a difficult problem to realize a cathode-ray tube suppressed in cost. These publications of cathode-ray tubes merely refer to the visual recognition of flatness in consideration of only the gap (distance in the tube axial direction) of the diagonal ends from the central part of the inner surface of the effective region of the panel, and nothing is considered about the visual recognition of flatness due to cylindrical shape of the inner surface of the effective region.
Incidentally, Jpn. UM (Utility Model). Publication No. 7-29566 discloses a cathode-ray tube, as shown in FIG. 7, for suppressing the distortion of image by forming a closed loop in the entire screen along a line 2 (equal thickness line) linking the points of equal wall thickness of the panel 1.
In such constitution, however, the horizontal axial end (X-axis end), vertical axial end (Y-axis end) and diagonal axial end (D-axis end) of the panel 1 are equal in wall thickness, and the effect of suppressing distortion by refraction of light rays in the panel 1 is lowered. Moreover, in the panel 1, peaks are formed near the diagonal axial ends, and when the viewpoint is moved, the peaks may be easily recognized visually. Further, in the case of the color cathode ray tube, when forming the effective surface of the shadow mask in a shape similar to the inner surface of the panel 1, the strength for holding the curved surface is weak in the marginal area of the equal thickness line, that is, in the flat region near the horizontal and vertical axial ends. It is hence regarded difficult to realize such color cathode ray tube.
Therefore, from the viewpoint of ease of seeing the image, the cathode-ray tube is desired to make the inner surface of the panel effective region and the fluorescent screen flat. However, when the inner surface of the panel effective region and the fluorescent screen are formed into flat, the strength of the vacuum envelope made of glass may not be sufficient. Still more, due to refractive index of the light rays in the panel glass, the floating phenomenon of image in the peripheral area of the screen may occur, and the visual recognition of the flatness may be impaired. In the color cathode ray tube, yet, the workability of the shadow mask may be decreased.
It is hence an object of the invention to provide a cathode-ray tube formed in a proper curved surface on the inner surface of a panel whose outer surface is a flat surface, capable of assuring the strength of the vacuum envelope, suppressing deterioration of visual recognition of flatness due to refraction of light rays in the panel glass, and, in a color cathode ray tube, further enhancing the workability of the color selecting electrode (shadow mask).
(1) In a cathode-ray tube having a panel whose outer surface is a flat surface and whose inner surface is a convex curved surface projecting in the outward direction from its center, and forming a substantially rectangular fluorescent screen on the inner surface of this panel, with an aspect ratio of M:N where M is the distance in the horizontal direction and N is the distance in the vertical direction, the inner surface of the panel is formed in a curved surface satisfying the following formulas                               Δ          ⁢                      xe2x80x83                    ⁢                      D            ⁡                          (              r              )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢                      H            ⁡                          (                                                M                                                                                    M                        2                                            +                                              N                        2                                                                                            ·                r                            )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢          D          ⁢                      xe2x80x83                    ⁢                      (                                          M                                                                            M                      2                                        +                                          N                      2                                                                                  ·              r                        )                                              (        10        )                                          Δ          ⁢                      xe2x80x83                    ⁢                      D            ⁡                          (              r              )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢                      V            ⁡                          (                                                N                                                                                    M                        2                                            +                                              N                        2                                                                                            ·                r                            )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢          D          ⁢                      xe2x80x83                    ⁢                      (                                          N                                                                            M                      2                                        +                                          N                      2                                                                                  ·              r                        )                                              (        11        )            
where xcex94H(r), xcex94V(r), xcex94D(r) are respectively gaps or difference along a tube axis on the horizontal axis, vertical axis and diagonal axis of the fluorescent screen at positions of distance r from the center of the inner surface.
(2) In the cathode-ray tube of (1), when the gap xcex94D(r) on the diagonal axis of the fluorescent screen of the panel is the maximum gap xcex94D(r Max), this gap xcex94D(r Max) is determined in a range of 5 mm to 20 mm.
(3) In a cathode-ray tube having a panel whose outer surface is a flat surface and whose inner surface is a convex curved surface projecting in the outward direction from its center, forming a substantially rectangular fluorescent screen composed of fluorescent layers of plural colors on the inner surface of this panel, with an aspect ratio of M:N where M is the distance in the horizontal direction and N is the distance in the vertical direction, and disposing a substantially rectangular color selecting electrode faced to this fluorescent screen, having a convex curved surface projecting in the direction of the fluorescent screen from its center, with an aspect ratio of this convex curved surface of M:N where M is the distance in the horizontal direction and N is the distance in the vertical direction, for selecting plural beams emitted from an electron gun by this color selecting electrode and displaying a color image on the fluorescent screen, the convex curved surface of the color selecting electrode is formed in a curved surface satisfying the following formulas                               Δ          ⁢                      xe2x80x83                    ⁢                      DM            ⁡                          (              r              )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢                      HM            ⁡                          (                                                M                                                                                    M                        2                                            +                                              N                        2                                                                                            ·                r                            )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢          D          ⁢                      xe2x80x83                    ⁢          M          ⁢                      xe2x80x83                    ⁢                      (                                          M                                                                            M                      2                                        +                                          N                      2                                                                                  ·              r                        )                                              (        12        )                                          Δ          ⁢                      xe2x80x83                    ⁢                      DM            ⁡                          (              r              )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢                      VM            ⁡                          (                                                N                                                                                    M                        2                                            +                                              N                        2                                                                                            ·                r                            )                                       greater than                   Δ          ⁢                      xe2x80x83                    ⁢          DM          ⁢                      xe2x80x83                    ⁢                      (                                          N                                                                            M                      2                                        +                                          N                      2                                                                                  ·              r                        )                                              (        13        )            
where xcex94HM(r), xcex94VM(r), xcex94DM(r) are respectively gaps on the horizontal axis, vertical axis and diagonal axis of the color selecting electrode at positions of distance r from the center of the convex curved surface.
(4) In the cathode-ray tube of (3), when the gap xcex94DM(r) on the diagonal axis of the color selecting electrode is the maximum gap xcex94DM(r Max), this maximum gap xcex94DM(r Max) is determined in a range of 5 mm to 20 mm.